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FTOS Configuration Guide for the C-Series - Force10 Networks

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Table 50 Regular Expressions<br />

Regular<br />

Expression Definition<br />

+ (plus) Matches 1 or more sequences of <strong>the</strong> immediately previous character or pattern.<br />

? (question) Matches 0 or 1 sequence of <strong>the</strong> immediately previous character or pattern.<br />

( ) (paren<strong>the</strong>sis) Specifies patterns <strong>for</strong> multiple use when followed by one of <strong>the</strong> multiplier<br />

metacharacters: asterisk *, plus sign +, or question mark ?<br />

[ ] (brackets) Matches any enclosed character; specifies a range of single characters<br />

- (hyphen) Used within brackets to specify a range of AS or community numbers.<br />

_ (underscore) Matches a ^, a $, a comma, a space, a {, or a }. Placed on ei<strong>the</strong>r side of a string to<br />

specify a literal and disallow substring matching. Numerals enclosed by underscores<br />

can be preceded or followed by any of <strong>the</strong> characters listed above.<br />

| (pipe) Matches characters on ei<strong>the</strong>r side of <strong>the</strong> metacharacter; logical OR.<br />

As seen in Figure 356, <strong>the</strong> expressions are displayed when using <strong>the</strong> show commands. Use <strong>the</strong> show<br />

config command in <strong>the</strong> CONFIGURATION AS-PATH ACL mode and <strong>the</strong> show ip as-path-access-list<br />

command in EXEC Privilege mode to view <strong>the</strong> AS-PATH ACL configuration.<br />

For more in<strong>for</strong>mation on this command and route filtering, refer to Filter BGP routes.<br />

Configure IP community lists<br />

Within <strong>FTOS</strong>, you have multiple methods of manipulating routing attributes. One attribute you can<br />

manipulate is <strong>the</strong> COMMUNITY attribute. This attribute is an optional attribute that is defined <strong>for</strong> a group<br />

of destinations. In <strong>FTOS</strong>, you can assign a COMMUNITY attribute to BGP routers by using an IP<br />

Community list. After you create an IP Community list, you can apply routing decisions to all routers<br />

meeting <strong>the</strong> criteria in <strong>the</strong> IP Community list.<br />

IETF RFC 1997 defines <strong>the</strong> COMMUNITY attribute and <strong>the</strong> pre-defined communities of INTERNET,<br />

NO_EXPORT_SUBCONFED, NO_ADVERTISE, and NO_EXPORT. All BGP routes belong to <strong>the</strong><br />

INTERNET community. In <strong>the</strong> RFC, <strong>the</strong> o<strong>the</strong>r communities are defined as follows:<br />

• All routes with <strong>the</strong> NO_EXPORT_SUBCONFED (0xFFFFFF03) community attribute are not sent to<br />

CONFED-EBGP or EBGP peers, but are sent to IBGP peers within CONFED-SUB-AS.<br />

• All routes with <strong>the</strong> NO_ADVERTISE (0xFFFFFF02) community attribute must not be advertised.<br />

• All routes with <strong>the</strong> NO_EXPORT (0xFFFFFF01) community attribute must not be advertised outside a<br />

BGP confederation boundary, but are sent to CONFED-EBGP and IBGP peers.<br />

<strong>FTOS</strong> also supports BGP Extended Communities as described in RFC 4360—BGP Extended<br />

Communities Attribute.<br />

<strong>FTOS</strong> <strong>Configuration</strong> <strong>Guide</strong>, version 7.7.1.0 495

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